In recent years, along with the advancement of the digital techniques in electronic devices, demands for increasing the capacity and data transfer speed on solid-state memory devices have been increasing for storage of data, such as a picture, and the like. To meet such demands, U.S. Pat. No. 6,204,139 discloses a technique for forming a solid-state memory device using a perovskite material whose resistance value varies according to an applied electric pulse (e.g., Pr(1-x)CaXMnO3(PCMO), LaSrMnO3(LSMO), GdBaCoXOY(GBCO), etc.). According to the technique disclosed in this publication, a predetermined electric pulse is applied to these materials (hereinafter, referred to as “variable-resistance material(s)”) to increase or decrease the resistance value of the materials. The resistance value which has varied as a result of application of the pulse is used for memorization of different values. Based on this scheme, the materials are used for memory devices.
Perovskite materials have been disclosed in U.S. Pat. No. 6,204,139 as a material whose resistance value varies according to an electric pulse. Also, a memory device has been proposed wherein a deep acceptor level and shallow donor level of an amorphous carbon film are used to vary the resistance by injection of charge (J. Appl. Phys., Vol. 84, (1998), p 5647).
Japanese Laid-Open Patent Publication No. 2004-342843 (Patent Document 2) discloses a technique relating to a nonvolatile memory device wherein a voltage is applied to an electrode formed of Ag or Cu on an amorphous oxide (e.g., an oxide formed by one or more elements selected from Ti, V, Fe, Co, Y, Zr, Nb, Mo, Hf, Ta, W, Ge, and Si) such that Ag or Cu, which is the material of the electrode, is ionized and diffused in a thin film, whereby the resistance value of the amorphous oxide is varied.
[Patent Document 1] U.S. Pat. No. 6,204,139
[Patent Document 2] Japanese Laid-Open Patent Publication No. 2004-342843
[Non-Patent Document] J. Appl. Phys., Vol. 84, (1998), p 5647